linux-kernel - Re: [PATCH] spi: dt-bindings: samsung: make dma properties not required

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Date: Sat, 2 Mar 2024 11:36:47 +0200
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Mark Brown <broonie@...nel.org>,
 Sam Protsenko <semen.protsenko@...aro.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc: andi.shyti@...nel.org, robh+dt@...nel.org, conor+dt@...nel.org,
 linux-spi@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 andre.draszik@...aro.org, peter.griffin@...aro.org, willmcvicker@...gle.com,
 kernel-team@...roid.com
Subject: Re: [PATCH] spi: dt-bindings: samsung: make dma properties not
 required



On 01.03.2024 22:42, Mark Brown wrote:
> On Fri, Mar 01, 2024 at 01:28:35PM -0600, Sam Protsenko wrote:
>> On Fri, Mar 1, 2024 at 5:55 AM Tudor Ambarus <tudor.ambarus@...aro.org> wrote:
> 
>>> Since the addition of the driver in 2009, the driver selects between DMA
>>> and polling mode depending on the transfer length - DMA mode for
>>> transfers bigger than the FIFO depth, polling mode otherwise. All
>>> versions of the IP support polling mode, make the dma properties not
>>> required.
> 
>> AFAIU, the device tree has nothing to do with drivers, it's about
>> hardware description. Does making DMA properties not required here

correct

>> mean that there are some HW out there which doesn't integrate DMA in

no, to me it means that the IP can work without DMA, only in PIO mode,
regardless if DMA is integrated or not. Not required means that the
property is not mandatory, which is what I'm trying to achieve here.

>> SPI blocks? Even if this change is ok (I'm not sure), the
>> argumentation doesn't look sound to me.

switching to PIO mode in the driver for sizes smaller than FIFO depths
in the driver guarantees that all existing compatibles support PIO mode.

Are you saying that if there is a physical line between an IP and DMA
controller, then the DMA properties must always be specified in dt? I
thought they can be marked as optional in this case, and that's what I
did with this patch.

> 
> I do remember there being some SoC which shipped a SPI controller in
> that configuration for some reason.  Possibly one of the OEM ones rather
> than one in a Samsung SoC?

with DMA you mean?

Thanks,
ta